Southern Ocean's Carbon Levels Shock Scientists

"Of all the CO2 emitted into the atmosphere, only half of it stays there; the rest goes into carbon sinks. There are two major natural carbon sinks: the oceans and the land 'biosphere'. They are equivalent in size, each absorbing a quarter of all CO2 emissions."

Southern Ocean drowning in carbon dioxide

Reuters News Service, May 17, 2007

WASHINGTON -- The Southern Ocean around Antarctica is so loaded with carbon dioxide that it can barely absorb any more, so more of the gas will stay in the atmosphere to warm up the planet, scientists reported on Thursday.

The phenomenon was not expected to be apparent for decades, Ms. Le Quere said in a telephone interview from the University of East Anglia in Britain.

"We thought we would be able to detect these only the second half of this century, say 2050 or so," she said. But data from 1981 through 2004 show that the sink is already full of carbon dioxide. "So I find this really quite alarming."

The Southern Ocean is one of the world's biggest carbon reservoirs, known as a carbon sink. When carbon is in a sink -- whether it is an ocean or a forest, both of which can lock up carbon dioxide -- it stays out of the atmosphere and does not contribute to global warming.

The new research, published in the latest edition of the journal Science, indicates that the Southern Ocean has been saturated with carbon dioxide at least since the 1980s.

This is significant, Ms. Le Quere said, because the Southern Ocean accounts for 15 per cent of the global carbon sink.

Winds from warming at core

Increased winds over the past half-century are to blame for the change, Mr. Le Quere said. These winds blend the carbon dioxide throughout the Southern Ocean, mixing the naturally occurring carbon that usually stays deep down with the human-caused carbon.

When natural carbon is brought up to the surface by the winds, it is harder for the Southern Ocean to accommodate more human-generated carbon, which comes from factories, coal-fired power plants and petroleum-powered motor vehicle exhaust.

The winds themselves are caused by two separate human factors.

First, the human-spawned ozone depletion in the upper atmosphere over the Southern Ocean has created large changes in temperature throughout the atmosphere, she said.

Second, the uneven nature of global warming has produced higher temperatures in the northern parts of the world than in the south, which has also made the winds accelerate in the Southern Ocean.

"Since the beginning of the industrial revolution, the world's oceans have absorbed about a quarter of the 500 gigatonnes (500 billion tonnes) of carbon emitted into the atmosphere by humans," Chris Rapley of the British Antarctic Survey said in a statement.

"The possibility that in a warmer world the Southern Ocean -- the strongest ocean sink -- is weakening is a cause for concern," Mr. Rapley said.

Another sign of warming in the Antarctic was reported this week by NASA, which found vast areas of snow melted on the southern continent in 2005 in a process that may accelerate invisible melting deep beneath the surface.

Polar ocean 'soaking up less CO2'

BBCNews.com, May 19, 2007

One of Earth's most important absorbers of carbon dioxide (CO2) is failing to soak up as much of the greenhouse gas as it was expected to, scientists say.

The decline of Antarctica's Southern Ocean carbon "sink" - or reservoir - means that atmospheric CO2 levels may be higher in future than predicted.

These carbon sinks are vital as they mop up excess CO2 from the atmosphere, slowing down global warming.

The study, by an international team, is published in the journal Science.

This effect had been predicted by climate scientists, and is taken into account - to some extent - by climate models. But it appears to be happening 40 years ahead of schedule.

The data will help refine models of the Earth's climate, including those upon which the predictions of the Intergovernmental Panel on Climate Change (IPCC) are based.

Of all the CO2 emitted into the atmosphere, only half of it stays there; the rest goes into carbon sinks.

There are two major natural carbon sinks: the oceans and the land "biosphere". They are equivalent in size, each absorbing a quarter of all CO2 emissions.

The Southern Ocean is thought to account for about 15% of all carbon sinks.

Sink efficiency

It was assumed that, as human activities released more CO2 into the atmosphere, ocean sinks would keep pace, absorbing a comparable percentage of this greenhouse gas.

The breakdown in efficiency of these sinks was an expected outcome, but not until the second half of the 21st Century.

Lead researcher Corinne Le Quere and colleagues collected atmospheric CO2 data from 11 stations in the Southern Ocean and 40 stations across the globe.

Measurements of atmospheric CO2 allowed them to infer how much carbon dioxide was taken up by sinks. The team was then able to see how efficient they were in comparison to one another at absorbing CO2.

"Ever since observations started in 1981, we see that the sinks have not increased [in their absorption of CO2]," Corinne LeQuere told the BBC's Science in Action programme.

"They have remained the same as they were 24 years ago even though the emissions have risen by 40%."

The cause of the decline in the Southern Ocean sink, the researchers explain, is a rise in windiness since 1958.

This increase in Southern Ocean winds has been attributed to two factors.

The first is the depletion of ozone in the upper atmosphere, which changes the temperature of this region.

The second is recent climate change, which warms the tropics more than the Southern Ocean.

Both these processes change atmospheric circulation over the Southern Ocean, resulting in stronger winds.

Churning waters

Oceans store much of their CO2 in deep waters. But, explained Dr Le Quere, "as the winds increase, the water in the ocean mixes more".

The British Antarctic Survey (BAS) scientist added: "The CO2 that would normally be in the deep ocean and would just stay there instead gets brought up to the surface and outgasses to the atmosphere."

The ocean surface becomes saturated with CO2 and cannot take up any more from the atmosphere.

Dr Sus Honjo, from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, US, is working on a separate project to assess the efficiency of the Southern Ocean carbon sink, using a different method.

He said recent developments in technology now made possible very detailed monitoring of marine carbon sinks, with some data available in real time.

"We have been way behind the modellers, who are hungry for numbers. But now we are starting to catch up because of the new tools and instruments available," he told BBC News.

Dr Honjo said recent evidence suggested the north-western Pacific appeared to be another significant CO2 sink.

As CO2 is absorbed by the oceans, it makes them more acidic, harming populations of marine organisms such as coral. The latest study suggests that phenomenon will only get worse over the century.

"The problem is that the extra CO2 from human emissions stays in the surface ocean and does not get removed to deep waters," said Dr Le Quere.

"So the problem gets worse, because the biological organisms affected by ocean acidification live, of course, at the surface where there is sunlight."